K562 is an erythroleukemic cell line used as a model for the study of the control of human globin gene expression. These cells do not support transcription of the beta-globin gene but do express transcripts of epsilon- and gamma-globin genes at very high levels when exposed to a number of inducing agents. Results from this and other laboratories suggest that the control of this pattern of expression is mediated by the presence and/or absence of trans-acting factors which exert their action on sequences corresponding to the promoters of these genes. We have previously reported the presence of a transcriptional control element with properties of a silencer extending from -392 to -177 bp relative to the cap site of the human epsilon-globin gene. We also showed that this silencer has stronger inhibitory activity in HeLa cells than K562 human erythroleukemia cells. Using deletion mutants and synthetic oligonucleotides in transient expression assays, DNA sequences responsible for this effect have been further delimited to 44 nucleotides located between -294 and -251 bp. Gel electrophoresis mobility shift assays and DNasel footprinting assays demonstrate that these negative regulatory sequences are recognized differently by proteins present in nuclear extracts obtained from HeLa and K562 cells. The protein present in K562 cells, but not in HeLa cells, that interacts specifically with this silencer binds to the same sequence recognized by the yeast binding protein ABF1. Possible mechanisms by which these proteins may regulate epsilon- globin gene transcription in erythroid and non-erythroid cells are discussed. We have constructed several mice using transgenic techniques that express both the human alpha-globin and beta-S-globin polypeptides at levels of 15- 20% of endogenous mouse hemoglobin. Data on erythrocyte functional properties now being studied include morphological analysis oxygen affinity curves, hematological parameters and rheology. Further cross breeding studies should result in a line of transgenic animals manifesting the sickle cell phenotype.